Many modern conveniences, such as radio, television, mobile telephones, and mobile data services, depend on reliable wireless communication technology. Since multiple services must co-exist within the same environment, it is critically important that the industrial high-power radio frequency broadcasting equipment supporting these services only transmit radio frequency energy within its appropriate allocated frequency band. A failure in RF broadcasting equipment to constrain its output frequencies could disrupt other wireless services, creating a major public inconvenience and resulting in potential consequences for the equipment operator.
This issue becomes more critical as the quantity of services crowding the common airwaves increases. Furthermore, since broadcasting equipment uses large quantities of energy, some types of failures can possibly result in physical damage, fire, explosions, and injury to nearby personnel.
It is common practice in the industry to use cross-coupling resonant filters, which provide a restrictive link conveying only the desired frequency bands. Energy in other undesired frequency bands is either not passed across the link, or is absorbed by the link and converted to heat. Multiple capacitors of appropriate values limit high frequencies from passing, while inductors limit low frequencies. Meanwhile, any remaining unwanted high frequency energy is dissipated as heat, and a central parallel inductive grounded loop dissipates unwanted low frequency energy. The interaction of these effects creates a narrowly defined range of frequencies that can make it through. The rate of energy loss of a filter is known as the quality factor or “Q” of the filter. If a larger “Q,” i.e., a lower rate of energy loss, is desired, without otherwise changing the behavior of the filter, in general the values of all the elemental components should be increased by the same factor. For example, you can double the size of the inductors and the capacitors. Unfortunately, doubling the sizes requires more physical space, which can be a problem, especially in devices where small size is important, such as mobile telephones.
Many variations of this concept exist, and it is well-known how to calculate the exact behavior of these devices in response to signals of various frequencies, using equations that consider the arrangement of the constituent elemental devices and their values. Some factors that must be taken into account when designing such filter include the quality factor needed, the amount of phase that can be shifted, and how much signal loss is permitted. However, conventional filters are not capable of handling high power applications while maintaining a desired coupling bandwidth. Further, conventional filters do not have adjustable cross-coupling and good thermal conduction while reducing high potential voltage.
Accordingly, there is a need and desire to provide a filter for handling high power applications with adjustable cross-coupling and good thermal conduction while reducing high potential voltage and maintaining desired coupling bandwidth.